# CVE-2026-99030: net: skbuff: don't leave stale bytes in skb_copy_and_csum_bits()


- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 23 Oct 2026
- **Updated:** 24 Oct 2026
- **Also known as:** BELL-CVE-2026-99030, DEBIAN-CVE-2026-99030, GHSA-2m74-g73v-pv5c, UBUNTU-CVE-2026-99030

## What is CVE-2026-99030?

CVE-2026-99030 is a high-severity vulnerability in Linux, published on 23 Oct 2026. 

### Official description

In the Linux kernel, the following vulnerability has been resolved:

net: skbuff: don't leave stale bytes in skb_copy_and_csum_bits()

When skb_copy_and_csum_bits() reaches unreadable frags it returns 0
after copying only the linear part, and the rest of the caller's buffer
is left as it was.  The callers copy into a buffer that is about to go
out on the wire: an ICMP error quoting the offending packet, or a
driver's TX bounce buffer in skb_copy_and_csum_dev().  Neither buffer
is zeroed beforehand, so whatever was in memory there gets sent.

Zero the part of the buffer we didn't fill.  The checksum usually
won't match the data any more, so the receiver will usually drop the
packet, but either way it no longer carries anything it shouldn't.
Only zero for a positive @len, a negative one from a broken caller must
not turn into a huge memset().

## Which versions are affected by CVE-2026-99030?


## How do I fix CVE-2026-99030?

Upgrade to a fixed version.

## Is CVE-2026-99030 being exploited?

There is no known exploitation of CVE-2026-99030 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-99030 and fix it if it is affected.

What it is: CVE-2026-99030 is a high-severity vulnerability in Linux, published on 23 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-99030 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-99030/ (Markdown: https://insights.sbomify.com/CVE-2026-99030/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-99030
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-99030
- OSV: https://osv.dev/vulnerability/CVE-2026-99030

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-99030/
Summaries are generated and may contain mistakes; the official description above is the record.